Shaking table testing of an existing masonry building: assessment and improvement of the seismic performance          下载免费PDF全文

Nuno Mendes  Paulo B. Lourenço  Alfredo Campos‐Costa 《地震工程与结构动力学》2014,43(2):247-266

This paper aims to assess and improve the seismic performance of an existing masonry building with flexible floors, representative of a Portuguese building typology—‘gaioleiro’ buildings. The study involved seismic tests and dynamic identification tests of two models (nonstrengthened and strengthened) in the shaking table. Each model was subjected to several seismic tests with increasing amplitude. Before the first test and after each seismic test, the dynamic identification of the model was carried out, aiming at obtaining their seismic vulnerability curves based on a damage indicator obtained from the decrease of the frequencies of the modes. In the strengthened model, steel elements were used to improve the connection between walls and floors, together with ties in the upper stories. The results show that adopted strengthening technique is effective for reducing the seismic vulnerability of ‘gaioleiro’ buildings, namely for improving the out‐of‐plane behavior of the facades. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Near-infrared sky background fluctuations at mid- and low latitudes     

G. Moreels  J. Clairemidi  M. Faivre  D. Pautet  F. Rubio da Costa  P. Rousselot  J.W. Meriwether  G.A. Lehmacher  E. Vidal  J.L. Chau  G. Monnet 《Experimental Astronomy》2008,22(1-2):87-107

The emission of the upper atmosphere introduces an additional variable component into observations of astronomical objects in the NIR 700–3,000 nm range. The subtraction of this component is not easy because it varies during the night by as much as 100% and it is not homogeneous over the sky. A program aimed at measuring and understanding the main characteristics of the atmospheric NIR emission was undertaken. A 512?×?512 CCD camera equipped with a RG780/2 mm filter is used to obtain images of the sky in a 36°?×?36° field of view. The intensities of a given star and of the nearby region devoid of star in a 439 arcmin² area are monitored during periods of time of several hours. The sky intensity measured in the 754–900 nm bandpass, reduced to zenith and zero airmass is comprised between mag20 and mag18.5 per arcsecond². A diminution by a factor of two during the night is frequently observed. Intensity fluctuations having an amplitude of 15% and periods of 5–40 min are present in the images with a structure of regularly spaced stripes. The fluctuations of the NIR sky background intensity are due to (1) the chemical evolution of the upper atmosphere composition during the night and (2) dynamical processes such as tides with periods of 3–6 h or gravity waves with periods of several tens of minutes. We suggest that a monitoring of the sky background intensity could be set up when quantitative observations of astronomical objects require exposure times longer than ~10 min. The publication is illustrated with several video films accessible on the web site http://www.obs-besancon.fr/nirsky/. Enter username: nirsky and password: skynir.  相似文献   

Shaking table testing for masonry infill walls: unreinforced versus reinforced solutions          下载免费PDF全文

Paulo B. Lourenço  João M. Leite  Manuel F. Paulo‐Pereira  A. Campos‐Costa  P. X. Candeias  Nuno Mendes 《地震工程与结构动力学》2016,45(14):2241-2260

Several factors influence the behaviour of infilled frames, which have been a subject of research in the past with moderate success. The new generation of European design standards imposes the need to prevent brittle collapse of the infills and makes the structural engineer accountable for this requirement, yet it fails to provide sufficient information for masonry infills design. Therefore, the present work aims at understanding the seismic behaviour of masonry infill walls within reinforced concrete frames, using both unreinforced and reinforced solutions (bed joint reinforcement and reinforced plaster). For this purpose, three reinforced concrete buildings with different infill solutions were constructed at a scale of 1:1.5, all with the same geometry, and were tested on the shaking table of the National Laboratory for Civil Engineering, Portugal. All solutions performed adequately for the design earthquake, with no visible damage. Still, the experimental tests show that the double‐leaf‐unreinforced infill walls underperformed during a large earthquake, collapsing out of plane by rotating as rigid bodies with multiple configurations. Also the reinforced concrete buildings collapsed, because of the adverse interaction with the infill walls. The infill walls with bed joint reinforcement and reinforced plaster did not collapse out of plane, because of their connection to the concrete frame, which is an essential requirement. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

MeMoVolc report on classification and dynamics of volcanic explosive eruptions     

C. Bonadonna  R. Cioni  A. Costa  T. Druitt  J. Phillips  L. Pioli  D. Andronico  A. Harris  S. Scollo  O. Bachmann  G. Bagheri  S. Biass  F. Brogi  K. Cashman  L. Dominguez  T. Dürig  O. Galland  G. Giordano  M. Gudmundsson  M. Hort  A. Höskuldsson  B. Houghton  J.C. Komorowski  U. Küppers  G. Lacanna  J.L. Le Pennec  G. Macedonio  M. Manga  I. Manzella  M. de’ Michieli Vitturi  A. Neri  M. Pistolesi  M. Polacci  M. Ripepe  E. Rossi  B. Scheu  R. Sulpizio  B. Tripoli  S. Valade  G. Valentine  C. Vidal  N. Wallenstein 《Bulletin of Volcanology》2016,78(11):84

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Evolution of earthquake losses in Portuguese residential building stock     

Maria Luísa Sousa  Alfredo Campos Costa 《Bulletin of Earthquake Engineering》2016,14(7):2009-2029

The evolution of the expected earthquake losses in different Portuguese regions was studied in order to determine whether the natural regeneration of buildings could contribute to the mitigation of seismic risk, although the building exposure has increased over time in most analysed regions. To achieve this goal, five inter-related risk indicators were estimated, based on the Portuguese censuses’ surveys of residential buildings and inhabitants obtained in two different moments in time: 2001 and 2011. The FEMA (2008) approach was used to estimate the risk indicators, i.e., the Annualized Economic and Human earthquake Losses, either in absolute terms or normalised by building and population exposure. This study offers a perspective of the seismic risk in the Portuguese mainland, provides a comparison of risk levels between different epochs, and analyses the obtained results in order to compare the risk among Portuguese regions. It is important to mention that the comparison of economic losses based on the building stocks surveyed in 2001 and in 2011 took into account the Portuguese inflation rate in that time interval. The main findings of the study show that the natural regeneration of the residential housing stock contributes to the reduction of the expected seismic economic losses in Portugal, at an average rate of 14 % per 10 years, and to the reduction of the expected annualized human losses to almost one half after 10 years. The results support the conclusion that the natural regeneration of the residential housing stock contributed to the mitigation of the seismic risk in mainland Portugal, in the 10 year period under analysis, even though there was an increase of the building exposure in the region.  相似文献   

Seismic vulnerability assessment and characterisation of the buildings on Faial Island, Azores     

Filipe Neves  Aníbal Costa  Romeu Vicente  C. Sousa Oliveira  Humberto Varum 《Bulletin of Earthquake Engineering》2012,10(1):27-44

The earthquake of the 9th of July 1998 that hit in the central group of the Azores archipelago greatly affected the islands of Faial, Pico and S?o Jorge, reaching a magnitude of Mw 6.2 with the epicentre located about 15km northeast of the Faial Island. This earthquake allowed the collection of an unprecedented quantity of data concerning the characterisation of the building stock and the damage suffered by construction. This is the main purpose of this research, consisting essentially of three main aspects: (i) A detailed characterisation of the building stock, assigning a five category classification, from old traditional rubble stone masonry to reinforced concrete moment framed buildings; (ii) A detailed damage grade classification based on the different damage mechanisms observed; and, (iii) A seismic vulnerability assessment of the building stock. The results of the vulnerability assessment together with the building stock database and damage classification were integrated into a GIS tool, allowing the spatial visualation of damage scenarios, which is potentially useful for the planning of emergency response strategies and retrofitting priorities to mitigate and manage seismic risk.  相似文献   

Out-of-plane behaviour of existing stone masonry buildings: experimental evaluation     

Alexandre A. Costa  António Arêde  Aníbal Costa  Carlos Sousa Oliveira 《Bulletin of Earthquake Engineering》2012,10(1):93-111

Masonry structures can be considered as the simplest type of structures concerning its assemblage but, at the same time, it is one of the most complex construction materials in terms of mechanical properties and correct behaviour assessment. In this context, the work herein presented aims at describing an experimental testing campaign recently carried out in order to characterize the out-of-plane behaviour of traditional masonry constructions. Taking advantage of the existence of a traditional two-storey masonry building abandoned after the 1998 Azores earthquake, several in-situ tests were defined and performed with the application of quasi-static cyclic loads at the building top level in the out-of-plane direction. In addition, the efficiency of retrofitting and/or strengthening techniques applied during the 1998 Azores reconstruction process was also experimentally evaluated. Finally, an overall discussion of these techniques is presented, resorting also to previous tests’ results carried out by the same authors, aiming at inferring and suggesting quantifications of strengthening techniques’ contributions for future interventions on existing buildings. For this purpose, simple analytical mechanical approaches were adopted in order to provide numerical estimates of strength that were found in good agreement with the experimental results.  相似文献   

Methods applied in studies of benthic marine debris     

Spengler A  Costa MF 《Marine pollution bulletin》2008,56(2):226-230

The ocean floor is one of the main accumulation sites of marine debris. The study of this kind of debris still lags behind that of shorelines. It is necessary to identify the methods used to evaluate this debris and how the results are presented and interpreted. From the available literature on benthic marine debris (26 studies), six sampling methods were registered: bottom trawl net, sonar, submersible, snorkeling, scuba diving and manta tow. The most frequent method used was bottom trawl net, followed by the three methods of diving. The majority of the debris was classified according to their former use and the results usually expressed as items per unity of area. To facilitate comparisons of the contamination levels among sites and regions some standardization requirements are suggested.  相似文献   

Development of a fish-based multimetric index to assess the ecological quality of marine habitats: the Marine Fish Community Index     

Henriques S  Pais MP  Costa MJ  Cabral H 《Marine pollution bulletin》2008,56(11):1913-1934

In this paper the Marine Fish Community Index (MFCI) for the assessment of ecological status of marine environment is proposed. The MFCI was divided into 4 typologies: Rocky subtidal; shallow, intermediate and deep soft-bottoms. Based on the typical community associated to each typology and the DPSIR analysis performed, a set of metrics were selected and tested through a multiple correlation matrix (Pearson’s coefficient) and the core ones included in the index. The MFCI was applied in all typologies and the scores obtained with each metric were analyzed. In order to test the robustness of the MFCI the final ecological value of each zone was recalculated by removing successively one metric at a time. The MFCI showed a sensitive and robust response in the ecological status assessment. Since it incorporates both functional and structural community information, the MFCI can be useful in the context of the Marine Strategy Framework Directive as well as in other contexts of conservation and sustainable management of the marine environment.  相似文献   

Vertical image waves in elliptically anisotropic media     

J.?SchleicherEmail author  A.?Novais  J.?C.?Costa 《Studia Geophysica et Geodaetica》2008,52(1):101-122

By reparameterization of the kinematic expressions for remigration in elliptically anisotropic media using a new ellipticity parameter, we derive a new image-wave equation in elliptically anisotropic media describing the position of the reflector as a function of the medium ellipticity. This image wave equation, which is a kind of medium-dependent one-way wave equation, can be used for automatically stretching a time-migrated image in depth until wells are tied or other given geologic criteria are met. In this way, it provides a useful means to use a priori depth information for finding an estimate of the vertical velocity, which cannot be detected from time processing only. Simple numerical examples confirm the validity of the image-wave equation even for nonconstant velocity.  相似文献